In the late stages of kidney disease it is often necessary for patients to repeatedly undergo dialysis where their blood is removed, cleansed in a dialysis machine and then returned to their bloodstream. Since arteries cannot be punctured numerous times during a dialysis process and remain functional, grafts are used. The grafts are implanted just below the patient's skin, typically on the patient's arm, to give the physician easy access to the artery and vein and the circulating blood. The graft can be easily palpated and punctured easily with needles so that the dialysis technician can access the patient's bloodstream.
Unfortunately, these grafts do not last long since they develop thrombosis and restenosis, particularly at the distal anastamosis. Wherever a graft is inserted, an injury repair process occurs, typically at the distal anastamosis where there is initially some thrombosis forming a matrix deposit. The cells migrate into that area, and the patient ends up developing a restenosis at the distal anastamosis. This stenosis developing in the distal anastamosis restricts the flow of blood flow through the graft. A blood clot will form proximal to that stenosis. The physician will usually then remove the blood clot from the graft with a balloon and then dilate the stenosis. The graft will stay open for awhile but the restenosis and rethrombosis process will reoccur, with the time interval between successive stenoses being shorter and shorter. After a few stenoses, the graft is considered a failure, requiring that the physician close the graft down and create a new one. Unfortunately, patients only have a limited number of sites where these grafts can be placed.
Stents have been used to maintain patency in stenosed dialysis access grafts. These stents are typically plain biliary stents. See, e.g., U.S. Pat. No. 5,591,226 (Trerotola et al.) U.S. Pat. No. 5,755,775 (Trerotola et al.), US 2004/0015180 (Yencho et al.) and George X. Zaleski, Brian Funaki, Jordan Rosenblum, Jennifer Theoharis and Jeff Leef, “Metallic Stents Deployed in Synthetic Arteriovenous Hemodialysis Grafts,” American Journal of Roentgenology 2001; 176:1515-1519. (The entire contents of these publications and all other publications mentioned anywhere in this disclosure are hereby incorporated by reference.) Examples of self-expanding stents that have been used in dialysis grafts include the Gianturco Z-stent (Cook) and the Wall Stent (Boston Scientific).
When the dialysis needles are inserted into the graft through the stent they will frequently impact the stent because the stent cell openings are very small. If the needle impacts the stent, it can dislodge it. It can also dull the needle, making it impossible to enter so that the needle has to be removed and reinserted, causing more trauma to the graft. Injury to stents after needle puncture has been observed. See, e.g., Lane et al., “Puncture-Induced Deforming of a Metallic Stent Within a Dialysis Access Graft Causing Thrombotic Failure: Case Report and Description of Salvage,” Journal of Vascular and Interventional Radiology 1998; 9:837-839. Lane et al. at page 839, recommends that one refrain from placing needle access in any dialysis graft segment containing a stent. This recommendation is based upon their observation that needle access deforms stents. See also, Rhodes and Silas, “Dialysis Needle Puncture of Wallgrafts Placed in Polytetrafluoroethylene Hemodialysis Grafts,” Journal of Vascular and Interventional Radiology 2005 16:1129-1134.
Accordingly, a new method and system for increasing the lives of dialysis grafts are needed.